1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly to a scheme for optimizing subchannel and bit allocation in a multicarrier-based mobile communication system.
2. Description of the Related Art
A multiple-input multiple-output (MIMO) system in the downlink can be broken down to multiple parallel independent single-user MIMO systems. Further, when the orthogonal frequency division multiple access (OFDMA) technology is applied to the downlink MIMO system, a multiuser-MIMO/OFDMA system is provided. In this system, data streams for users are multiplexed over space and frequency, and thus the users receive the spatially multiplexed data streams.
FIG. 1 is a conceptual diagram illustrating subchannels of a multiuser-multiple-input multiple-output/orthogonal frequency division multiple access (MIMO/OFDMA) system. In the multiuser-MIMO/OFDMA system as illustrated in FIG. 1, there are space division multiple access (SDMA) subchannels in which each user occupies several MIMO subchannels, for each orthogonal frequency division multiplexing (OFDM) subcarrier. The users generate MIMO subchannels using the MIMO technologies, and transmit data through the generated MIMO subchannels. A more important feature of a multiuser-MIMO/OFDMA system design is that SDMA channels are allocated to users, and bits are loaded to the MIMO subchannels allocated to a single user for adaptive modulation.
For subchannel and bit allocation, optimal and suboptimal schemes have been proposed to minimize the overall transmission power under the data rate constraint or to maximize a data rate under the transmission power constraint. For a multiuser-multiple-input single-output (MISO)/OFDM system, a bit allocation scheme for maximizing a signal-to-noise ratio (SNR) has been proposed. More specifically, a suboptimal scheme that takes into account interference and a data rate in a multiuser-MISO/OFDMA system has been proposed. However, when the data rate constraint is present, there is a drawback that the suboptimal scheme can be applied only to an OFDMA system.